Refining crude fatty acid monoglyceride



United States Patent Office Patented Aug. 21, 1956 REFINING CRUDE FATTY ACID MONOGLYCERIDE Ralph Miller, Woodside, N. Y., assignor to The Chemical Foundation, Incorporated, a New York membership corporation No Drawing. Application February 2, 1949, Serial No. 74,229

8 Claims. (Cl. 260-4101!) monoglycerides and diglycerides result in products containing a relatively low content of the desired substance. In most instances the other components of the mixture are unobjectionable. Since the utility of fatty acid partial esters is great even though the concentration be small,

millions of pounds of these mixtures are produced every earn 1 y A major object of this invention is to produce in concentrations that exceed those now marketed fatty acid partial esters of fatty acid mixtures.

A further object of this invention is to produce fatty acid partial esters more economically than is possible by known methods.

As is known, there are a variety of methods which can be utilized to form mixtures containing fatty acid partial esters. One general method involves the esterification of a polyhydric alcohol with a fatty acid or mixture of fatty acids in the presence of an esterification catalyst. Another method involves the reaction between a polyhydric alcohol and a fatty acid ester in the presence of an alcoholysis catalyst. The fatty acid ester may be the ester of a mono or polyhydric alcohol. Monoglycerides are perhaps the most important type of fatty acid partial ester with which this invention is concerned. The commercial monoglycerides produced at this time contain a lower monoester content than commercial fatty acid partial esters of glycol, or propylene glycol or diethylene glycol. For these reasons it is particularly appropriate to describe this invention in terms of the production of monoglycerides.

As noted above, one process in general use for the commercial production of monoglycerides is the esterification of glycerine with free fatty acids in the presence of a catalyst. The catalyst may be either alkaline or acidic or a catalytically active salt. Typical alkaline catalysts are sodium and potassium hydroxide, the alkali carbonates, alkyli alcoholates, lime, barium hydroxide and similar materials. Suitable acidic catalysts are sulfuric acid, phosphoric acid, hydrogen chloride, sulfur dioxide, boron trifluoride, etc. In addition, salts such as hydrated zinc chloride and hydrated stannous chloride are effective esterification catalysts. Theoretically, an equimolar mixture of fatty acid and glycerine is required to produce a monoglyceride. When such a ratio ofv glycerine to fatty acid is employed, the resulting mixture contains a relatively small percentage of monoglyceride. By increasing the ratio of glycerine to fatty acid, the monoglyceride content of the resulting mixture is increased. Irrespective of how great the ratio of glycerine to fatty acid is made, there is little advantage in having the mol ratio of glycerine to fatty acid exceed 3 to 1. When such a ratio is employed, the resulting mixture contains about 45% monoester. This is the usual commercial product.

A second method in general use is the alcoholysis of a triglyceride with glycerine using not more than about 20 parts of glycerine for every parts of fatty oil. The reaction is carried out in the presence of an alcoholysis catalyst such as caustic soda or potash or an alkali alcoholate. Many other substances will also catalyze the reaction. In carrying out the alcoholysis superior results are obtained in the absence of moisture in the reactants. Temperatures in the range 100 to 220 C. are employed. The mixture which results also contains about 45% monoester. Suitable fatty oils for use in this method of forming monoglycerides are marine oils such as fish, fish liver, and whale oil; vegetable oils such as linseed oil, soybean oil, coconut oil, palm oil, corn oil, cottonseed oil, etc.; and animal oils such as lard and tallow. Increasing the ratio of glycerine to fatty oil does not materially increase the monoester content of the product.

The reason the monoester content in each'instance is about 45 is due to the fact that the acyl radicals are distributed in random fashion among the available hydroxyl groups. As a consequence of this characteristic of the reaction, when fatty acids are esterified with glycerine using a ratio of glycerine to fatty acid larger than 1 to 1, the resulting mixture is composed of free fatty acid, monoglycerides, diglycerides, triglycerides and glycerine. Similarly, when a triglyceride is alcoholyzed with glycerine, the resulting mixture is composed of glycerine, monoglycerides, diglycerides, and triglycerides. The reason that any appreciable increase in the ratio of glycerine to triglyceride above 1 to 5 by weight or an increase in the mol ratio of glycerine to fatty acid of 3 to 1 does not raise the percentage of monoester formed is due to the limited miscibility of glycerine with fatty acids, triglycerides, and diglycerides. The hydroxyl groups of glycerine which are not in the same phase with the acyl radicals are not available for reaction and hence do not influence the reaction. The limited miscibilityof glycerine with the other components present in the reaction mixture automatically limits the ratio of glycerine to fatty oil or fatty acid that can be used to advantage.

By carrying the reaction out at elevated temperature, the solubility of glycerine in the reacting mixture is increased so that high temperatures tend to increase the monoester content of the product. The thermal stability of glycerine is limited so that when temperatures above about 220 C. are employed, undesirable substances are formed.

It is possible to use an extraneous solvent to increase the monoester content of the product. The employment of an extraneous solvent, however, introduces additional complications and expense. Moreover, the removal. of the extraneous solvent usually has to be carried out at elevated temperatures. Since monoglycerides tend to form diglycerides with the liberation and volatilization of glycerine at high temperatures, unless extraordinary precautions are observed, the use of extraneous solvents is self-defeating.

It is known to the art that the optimum range of ratio of glycerine to fat or fatty acid; temperature; catalyst concentration; time of reaction; etc. for the production of monoglycerides is limited. Some of the reasons why the optimum range of these variables is limited have been outlined above. One way by which the objectives of this invention can be achieved is to economically separate the reaction mixture into two or more fractions, one of which is high in monoester content. The reason that the objectives of this invention are attained by the economic isolation of a fraction with a high monoester content is that the balance of the original mixture may be recycled the manner described above.

It has now been found that mixtures of glycerine,'

monoglycerides, diglycerides, triglycerides and free fatty acids or such mixtures without any appreciable content of free fatty acids may be fractionated into two or more fractions with different properties by employing liquefied, normally gaseous hydrocarbons as selective solvents under controlled conditions. When the desired product is a fraction with a high monoester content, it is preferred to prepare an initial mixture containing from 40 to 50% of monoglyceride. The mixture is then divided into three fractions, one of which has a high monoester content. The low monoester content fractions are combined, additional glycerine and fatty acid added to the mixture to secure the optimum ratio of hydroxyl groups to acyl groups, the catalyst concentration adjusted if necessary, the mixture heated to reaction temperature and maintained at the reaction temperature until equilibrium is substantially reached.

The marked selectivity of this type of solvent when employed under the proper conditions is illustrated by the results obtained by the following procedure:

A sample of a typical commercial monoglyceride containing about 42% monoglyceride, a slightly lesser quantity of diglyceride, about of triglyceride and free fatty acid and the balance glycerine was placed in a steel bomb. Liquefied propane was added to the bomb until the ratio by weight of propane to charge was 10 to l. The contents of the bomb were warmed to about 115 F. Under these conditions substantially all the charge dissolved in the solvent. The bomb and its contents were then warmed to 130 F. Under these conditions a second liquid phase formed. This second liquid phase was denser than the solution from which it had separated and hence formed a bottom layer. It was also darker in color. The bottom layer was permitted to flow through a valve out of the bottom of the bomb into a container. The propane dissolved in the more dense phase was permitted to vaporize and the nonvolatile portion of the more dense phase retained for analysis. The bomb and its contents were heated to 150 F. This caused an additional amount of material to come out of solution. The material which had come out of solution between 130 F. and 150 F. was removed from the bomb in The bomb and its contents were heated to 180 F. and the material which came out of solution between 150 F. and 180 F. was removed from the bomb. The material which constituted the less dense phase at 180" F. was then removed from the bomb. In this way the original sample was divided into four fractions, namely, the material contained in the more dense phase formed at 130 F.; the material contained in the more dense phase formed in the temperature interval 130 F.-150 F.; the material contained in the more dense phase formed in the temperature interval 150 F.-180 F. and the material contained in the less dense phase at 180 F. The weight balance in this particular experiment was 99%. The yields and analytical constants of each fraction were as follows:

A similar experiment was carried out with a monoglyceride preparation produced under very special conditions to produce a product containing about 54% monoglyceride, 33% diglyceride, about 4% of triglyceride and fatty acid and the balance glycerine. A weight balance was obtained in this experiment of 93.5%. The results were as follows:

Yield, Saponlllca- Aeetyl Fraction Percent tion Value Number Less Dense 180 F 21. 7 188 111 From these results it can be seen that liquefied, normally gaseous hydrocarbons such as propane have the ability to dissolve substantially completely mixtures of mono, di and triglycerides at temperatures considerably below the critical temperature of the solvent but that increasing the temperature will cause these solvents to lose their solvent power for these substances selectively. That is, as the temperature is increased above the maximum temperature at which the solvent and mixture are completely miscible, the solvent appears to lose its ability to dissolve monoglycerides more rapidly than it loses its ability to dissolve diglycerides and triglycerides. Thus, it can be seen that the constituents in the mixture are fractionated with respect to acetyl number. Since monoglycerides have higher acetyl numbers than either diglycerides or triglycerides, the complex mixtures may be resolved into fractions which differ appreciably with respect to their monoglyceride content. The small amount of glycerine usually present in these mixtures tends to accumulate in the least soluble fraction. This batch method of operation while feasible is not eificient and does not permit as sharp a separation as is desirable.

The fractionation of .the monoglyceridecontaining mixture is preferably carried out in a liquid-liquid extraction system adapted for continuous counter-current operation. Towers equipped with batlles, packing or other contacting devices are particularly suitable. In addition to the extraction towers, the system should include pumps, instruments, means for controlling the temperature within the extraction tower and solvent recovery equipment. Plants able to handle liquefied, normally gaseous hydrocarbons safely and etliciently in solvent extraction processes of the type with which this invention is concerned are readily constructed. The pressures involved, of the order of 800 pounds per square inch, are moderate. The temperatures will rarely exceed 400 F. and usually will be far lower. The preferred solvent is propane although solvents containing other liquefiable, normally gaseous hydrocarbons may also be used. Such solvents may be composed of or in part of ethane, propylene, iso and normal butane, iso and normal butylene and others in this class.

When propane is employed, a two tower solvent extraction system is used to fractionate a monoglyceridecontaining mixture into three fractions at temperature levels between about 95 and 205 F. In one fraction the glycerine will be concentrated along with some of the monoglyceride; the second fraction will be composed primarily of monoester; the third fraction will be composed principally of diglycerides. In the diglyceridecontaining fraction, the relatively small percentage of triglycerides and free fatty acids will be concentrated.

A ratio of 10 parts or more of solvent to charge is used. The propane is introduced into the first tower close to the bottom of the tower. The charge is intro duced into the same tower somewhat above its midpoint. The temperature is controlled so that the temperature at the top of the tower is about 140 F. The temperature is maintained at about F. at the base of the tower. 'Ihe propane is less dense than the glyceride mixture and flows up the tower contacting the down-flowing glyceridemixture. Substantially all the fatty acid, triglyceride, diglyceride and most of the monoglyceride in the charge dissolves in the up-flowi-ng solvent. Most of the glycerine and a small amount of monoglyceride plus a small amount of propane leaves the tower through the bottom outlet.

The solvent phase leaves the first tower at the top and is introduced into the second tower at approximately half-way between the top and bottom of the tower. The propane solution from the top of the first tower is heated to approximately 165 F. before entering the second tower. Additional propane is introduced into the second tower close to the bottom of the tower. About parts by weight of propane to l of charge is employed. The temperature at the bottom of the tower is maintained at about 160- F. A temperature of about 185 F. is maintained at the top of the second tower. Most of the monoglyceride in the feed to the second tower is immiscible in the solvent at the elevated temperature so that it forms a second more dense liquid phase which flows down the tower counter-current to the rising stream of propane. Any fatty acid, diglyceride or triglyceride in the charge which tends to accompany the more dense monoglyceride phase is extracted by the rising propane. The propane phase leaves the top of the second tower and flows to a distillation system in which the propane is distilled and recovered. The monoglyceride phase after leaving'the bottom of the second tower is split into two streams. One stream is introduced to the first tower close to the top as reflux. The other stream flows to the solvent recovery system and the" propane associated with the monoglyceride phase is removed, recovered and recycled. The more dense phase which leaves the base of the first tower can either flow to a separate still in which the propane associated with it is removed and recovered or it can be fed to the same still in which the propane which leaves the top of the second tower is recovered.

The monoglyceride recovered from the stream that leaves the base of the second tower is the desired product. Since the other two fractions of the fractionation process are to be reacted again to form additional monoglyceride, it is possible to operate the process so that a high monoester content product is obtained. The monoester present in the other fractions is not lost. It is merely recycled. Therefore, there is no urgent necessity to attempt to obtain high yields of product. in the fractionation part of the process.

In many instances and particularly when the monoglyceride is to be incorporated into shortening, it is necessary that the catalyst used in the monoglyceride production reaction be removed from the final product. Since monoglycerides are excellent emulsifying agents, the removal of the catalyst is usually a troublesome operation. In many instances reagents are consumed in removing the catalyst or in inhibiting its activity. In the present process the catalyst need not be removed from the reaction mixture prior to subjecting the reaction mixture to fractionation. The catalyst is concentrated in the fraction which leaves the bottom of the first tower. Since this fraction including its catalyst content is recycled back to the monoglyceride production operation, this method of procedure not only effectively separates the catalyst from the final product but decreases the consumption of catalyst and avoids the ex penditure of additional reagents employed in other processes to enable the catalyst to be removed from the final product.

Although a preferred method of utilizing my discovery of the selective solubility characteristics of liquefied, normally gaseous hydrocarbons for fractionating mixtures containing mono, di and triglycerides has been described, the selective solubility characteristic of this type of solvent may be employed in other ways. A batch, counter-current method of operation can be employed or even in some cases, -a one stage, batch operation. While a temperature gradientpossesses advantages when an extraction tower is employed, good results can be obtained if the temperature is maintained at approximately the same level throughout the length of an extraction tower.

It can be seen that liquefied, normally gaseous hydrocarbons can be used to separate mixtures composed of mono, di and triglycerides into fractions with different properties when employed in the temperature range at which the solubility of these substances in these solvents decreases with an increase in temperature. The maximum temperature is approximately the critical temperature of the solvent. The minimum temperature is not more than about to F. below the critical temperature. The components in the mixture with the higher acetyl number come out of solution at the lower temperature. The pressure must be sufliciently high to maintain the solvent in the liquid phase while it is in contact with the mixture being fractionated. Higher pressures may be employed to simplify ease of control of the process. The hitherto unknown selectivity of this type of solvent for fractionating these mixtures when employed under the described conditions is the basis for the claims made hereunder.

I claim:

l. A process of refining crude fatty acid monoglyceride material containing unesterified glycerol, diglycerides and triglycerides which comprises intimately contacting crude fatty acid monoglyceride with a liquefied hydrocarbon solvent which is gaseous at ordinary temperature and pressure, the ratio of solvent to crude monoglyceride material being at least about 10:1 by weight and the temperature being between about 65 C. and the critical temperature of the solvent to form two liquid phases, one comprising relatively pure fatty acid monoglyceride I material and the other comprising principally the impurities, and separating the phases.

2. A process of refining crude fatty acid monoglyceride material containing unesterified glycerol, diglycerides and triglycerides to recover relatively pure fatty acid monoglyceride material which comprises intimately contacting about one part by weight of crude fatty acid m0noglyceride material with about 10 parts by weight of a liquefied hydrocarbon solvent, which is gaseous at ordinary temperature and pressure, at a temperature between about 65 C. and the critical temperature of said solvent to form two liquid phases, one comprising relatively pure fatty acid monoglyceride material and the other comprising principally the impurities, separating said phases and recovering said relatively pure fatty acid monoglyceride.

3. A method of treating a complex mixture derived from the catalytic reaction of glycerine with triglyceridecontaining material and which mixture cointains glycerine, mono, di and triglycerides to produce a fraction enriched in monoglycerides which comprises contacting such mixture with a liquefied, normally gaseous hydrocarbon solvent at a temperature above that at which the mixture is completely miscible and within the temperature range at which the glycerine is less soluble in the solvent than the glycerides and at a pressure sufliciently high to maintain the solvent in liquid phase to thereby form two immiscible liquid phases, the more dense phase being comprised of the bulk of the glycerine, a minor portion of the monoglycerides and some solvent and the less dense phase being comprised of the bulk of the solvent and the prepondcrant amount of the glycerides of the charge material; separating the said two immiscible phases; removing the contained solvent from the more dense phase and recycling the residue for further catalytic reaction with triglyceride-containing material; increasing the temperature of the said separated less dense phase to a point at which the monoglycerides are less soluble in the solvent than the di and triglycerides to thereby form two immiscible phases of different densities in the more dense phase of which the monoglycerides are largely concentrated, separating such monoglyceride-enriched more dense phase from the monoglyceride-denuded less dense phase and recovering a monoglyceride-enriched fraction from the separated more dense phase.

4. Aprocess in accordance with claim 3 in which the liquefied hydrocarbon is propane.

5. A process in accordance with claim 4 in which the ratio of solvent to the complex mixture is about to 1 by weight and in which the first said temperature range is between substantially 120-140 F. and the second temperature range is between approximately l60-185 F.

6. A method of producing a fraction enriched in monoglycerides from a mixture comprised of mono-, diand triglycerides which comprises contacting such mixture with a liquefied, normally gaseous hydrocarbon solvent, the ratio of liquefied, normally gaseous hydrocarbon solvent to said glyceride mixture and the contacting temperature being selected to form two immiscible liquid phases difiering in density, said temperature being higher than the highest temperature at which the solvent and the glyceride mixture are completely miscible at the selected ratio, the less dense phase containing the bulk of the solvent and a portion of the initial glyceride mixture enriched in diand tri-glycerides, the more dense phase containing the remainder of the solvent and the initial glyceride mixture said remainder of the initial glyceride mixture being enriched in monoglycerides, separating the less dense phase from the more dense phase and recovermg from the separated more dense phase a fraction enriched in monoglycerides.

7. The process of claim 6 in which the liquefied hydrocarbon is propane.

8. A method of treating a complex mixture containing mono-, diand triglycerides to produce a fraction enriched in monoglycerides which comprises contacting such mixture with liquid propane, the ratio of liquid propane to the complex mixture being about 10 to 1 by weight, at a temperature between about F. and F. to form two immiscible liquid phases of different density, the less dense phase containing most of the propane and diand triglycerides, the more dense phase containing the remainder of the propane and diand triglycerides and most of the monoglycerides, separating the less dense phase from the more dense phase and recovering a fractilclm enriched in monoglycerides from the more dense p ase.

References Cited in the file of this patent UNITED STATES PATENTS 2,219,652 Hixson Oct. 29, 1940 2,290,609 Goss July 21, 1942 2,454,638 Dickinson et a1 Nov. 23, 1948 2,553,288 Young et al May 15, 1951 

1. A PROCESS OF REFINING CRUDE FATTY ACID MONOGLYCERIDE MATERIAL CONTAINING UNESTERIFIED GLYCEROL, DIGLYCERIDES AND TRIGLYCERIDES WHICH COMPRISES INTIMATELY CONTACTING CRUDE FATTY ACID MONOGLYCERIDE WITH A LIQUEFIED HYDROCARBON SOLVENT WHICH IS GASEOUS AT ORDINARY TEMPERATURE AND PRESSURE, THE RATIO OF SOLVENT TO CRUDE MONOGLYCERIDE MATERIAL BEING AT LEAST ABOUT 10:1 BY WEIGHT AND THE TEMPERATURE BEING BETWEEN ABOUT 65* C. AND THE CRITICAL TEMPERATURE OF THE SOLVENT TO FORM TWO LIQUID PHASES, ONE COMPRISING RELATIVELY PURE FATTY ACID MONOGLYCERIDE MATERIAL AND THE OTHER COMPRISING PRINCIPALLY THE IMPURITIES, AND SEPARATING THE PHASES. 